Exemplary embodiments of the present invention relate to a constant-current-drive LED module device, and more particularly, to an LED module device driven with constant current.
A luminescent diode (LED) may be operated only when constant current is stably supplied to a current drive element. In particular, as the LED demanding high power requires large drive current (generally, 350 mA or more), the LED generates a significant amount of heat and as a result, has degradation in luminance larger than the LED driven with low power.
This is directly connected with a lifespan of the LED and acts as very important factors in a lighting market. Therefore, all the LEDs driven with high power are driven with constant current and are driven by a pulse width modulation (PWM) scheme so as to more efficiently use power of a switching mode power supply (SMPS) that is used as a constant-current power source.
However, the PWM scheme requires electronic components, which leads to an increase in manufacturing costs. Therefore, a scheme for rectifying an alternating-current power source and applying it to the serially connected LED modules has been used in recent.
FIG. 1 illustrates a unidirectional LED module device in accordance with the related art.
The unidirectional LED module device in accordance with the related art includes a bridge diode 120 rectifying an input alternating-current power source 110 and a unidirectional LED module 130 connected to the bridge diode 120 through a resistor R1.
In this configuration, the resistor R1 determines a magnitude in current flowing in the unidirectional LED module 130.
FIG. 2 illustrates a waveform diagram of input voltage and driving current at the unidirectional LED module in accordance with the related art, wherein i is a current waveform flowing in a front end of the bridge diode 120 according to input AC voltage.
When a magnitude in voltage is a forward threshold voltage or more of the LED module 130 at a positive half-period voltage of the AC power source 110, current flows, such that the LED module 130 is light-emitted. Similarly, when the magnitude in voltage is the forward threshold voltage or more of the LED module 130 even at a negative half-period of the AC power source 110, current flows, such that the LED module 130 is light-emitted.
That is, as illustrated in FIG. 2, load current does not flow in period a and period b.
FIG. 3 illustrates a unidirectional LED module device in accordance with the related art.
The bidirectional LED module in accordance with the related art includes and a bidirectional LED module 220 that is connected to an input alternating-current power source 210 through the resistor R1.
In this configuration, the resistor R1 determines a magnitude in current flowing in the positive LED module 220.
FIG. 4 illustrates a waveform diagram of input voltage and driving current at the bidirectional LED module in accordance with the related art, wherein V is an voltage waveform and i is a current waveform flowing in the resistor R1 according to input alternating voltage, which is the same as FIG. 2.
As described above, a power factor may be low, total harmonic distortion (THD) may be increased, and a flicker phenomenon may excessively occur, due to operating characteristics of the LED module operated only when the magnitude in the input voltage is the forward threshold voltage or more, that is, the operating characteristics of the LED module by suddenly flowing current due to the conduction of the LED module when the magnitude in the input voltage is the forward threshold voltage or more of the LED module forward connected by the input of the AC power source, the short operating period of the LED module within one period of the AC power source, and the like. As a result, light efficiency may be degraded.